main() {
  //变量
  var name = '张三';
  print(name);
  var age = 18;
  print(age);
  age++;
  print(age);
  //常量
  const BASE_URL = 'https://www.baidu.com';
  print(BASE_URL);
  //常量可以在定义时赋值，也可以在运行时赋值
  const PI = 3.14;
  print(PI);
  final PI2 = 3.1415926;
  print(PI2);
}
